Apparatus for over-head service work



April 1957 M. E. MITCHELL APPARATUS FOR OVER-HEAD SERVICE WORK 4 Sheets-Sheet 1 Filed Dec. 30, 1952 A mm M 5 HI'TOEIVEYS.

April 1957 7 M. E. MITCHELL 2,787,278

APPARATUS FOR OVER-HEAD SERVICE (NORK Filed Dec. 50, 1952 4 Sheets-Sheet 2 INVENTOR. MHURICE EMITCHELL,

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April 1957 M. E. MITCHELL 2,787,278

APPARATUS FOR OVERHEAD SERVICE WORK Filed Da es; so, 1952 I 4 Sheets-Sheet 3 MquE/cL-Li Mrc/mz z,

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April. 2, M MlTCHELL APPARATUS FOR OVER-HEAD SERVICE WORK Filed Dec. 50, 1952 v 4 Sheets-Sheet 4 Reservoir .92 0 Oui B 233 7 Motor:

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APPARATUS FOR OVER-HEAD SERVICE WORK Maurice E. Mitchell, Muncie, Ind., assignor to Mitchell Maintenance Company, Inc., Muncie, Ind, a corporation of Indiana Application December 30, 1952, Serial No. 328,590

18 Claims. (Cl. 134-415) This invention relates to self-propelled apparatus for performing over-head service work in industrial establishments, especially for performing over-head washing services as of light fixtures, ceilings, and the like.

It is the primary object of the invention to provide a self-propelled vehicle equipped with a lift platform which rises at an angle, to carry a Workman to a position for overhead service, as in industrial plants where the floor area is obstructed by industrial equipment. It is an object of the invention to provide self-propelled appa ratus for supporting a platform in a projected overhanging position, and to raise and lower the platform between that position and a lowered position for travel. it is an object of the invention to provide such equipment in which the platform can be adjusted to any convenient height between its two extreme positions and may be traversed relative to its supporting structure between a projecting position and a retracted position. It is the general object of my invention to facilitate overhead service work in an industrial establishment, and further more specific objects of the invention will appear from the following description and the accompanying drawings.

in accordance with the invention, a platform is carried by inclined elevating mechanism and is preferably supported thereon by traversing mechanism to permit it to be moved horizontally at any elevated position. The elevating and traversing mechanisms are desirably powered, and controlled by controls accessible to the workman on the platform. Such mechanism is mounted on a suitably self-propelled vehicle, conveniently a modified industrial truck. The overhanging platform is counterbalanced, at least in part, by a water tank containing a flexible partition or bladder to form separate containers therein of relatively variable size. One container, conveniently that enclosed by the bladder, may originally occupy substantially the entire space within the tank and it may contain fresh wash water, and as that wash water is used, it is disposed of by return to the other container, conveniently the space between the bladder and the tank walls, so that the tank as a whole will contain a substantially constant amount of water for counterbalanclng purposes. The platform desirably carries one or more wash tanks, and a pump is provided to transfer the water to them from the counterbalance or ballast tank. The platform may also carry a tray for various items of washing equipment and for service tools and parts, and is desirably provided with retractable drop-cloth panels to protect underlying equipment when the platform is in use.

The accompanying drawings illustrate the invention. in such drawings:

Fig. l is a side elevation of apparatus embodying the invention, with the platform shown in full lines in its raised and projected position, and shown in dotted lines in a retracted position and in a lowered position;

Fig. 2 is an end elevation of the platform. in. raised position;

nite States Patent 2,787,278 Patented Apr. 2, 1957 Fig. 3 is a plan view of the apparatus shown in Fig. 1, with the platform in lowered position;

Fig. 4 is an end elevation of the ballast tank and its associated parts;

Fig. 5 is a longitudinal section of the apparatus shown in Fig. 4;

Fig. 6 is a plan view of the apparatus shown in Fig. 4;

Fig. 7 is a vertical section taken on the line 77 of Fig. 8 showing the platform supporting structure and drive;

Fig. 8 is a longitudinal section taken on the line 8-8 of Fig. 7;

Fig. 9 is a normal section showing the elevator mechamsm;

Fig. 10 is a diagram of the power drive and control for the elevator mechanism; and

Fig. 11 is a diagram of the power drive and control for the platform traverse mechanism.

The apparatus shown in Fig. l is built around the chassis of a commercial industrial lift truck, specifically alift truck model TIP-20 manufactured by the Barrett- Cravens Co. of Chicago, Illinois. That lift truck chassis is carried on a pair of spaced load wheels Ill, a central drive wheel 12, and a pair of spaced caster wheels 14, and it carries a motor-drive assembly 16 powered by an electric battery 18. The normal driving and steering mechanisms of the truck are used, but are controlled by a tiller handle 20 mounted at the top of anextension steering post 22 and carrying a set of push-buttons 21, all in position to be operated by a service man on the lowered platform. Normally, the tiller handle 24 lies in elevated position as shown in full lines, in which position it sets the brakes on the truck. The push-buttons 21 control forward and reverse operation of the truck. The tiller handle 20 is movable from its elevated position to a lowered position as shown in dotted lines in Fig. 1, where it releases the brakes and permits operation of the motor-drive 16 by the push-buttons. Lateral swinging movement of the handle 20 steers the truck.

An extension lift mechanism or column 30 is mounted on the truck frame adjacent the load wheels 10. The lift mechanism itself is substantially identical with that normally provided on the industrial lift truck, but is reversed to put its lift section 32 on the right or top side of its fixed section 34 instead of on the other side thereof. Whereas the lift mechanism 30 has an adjustable inclina tion in the standard lift truck, it is preferably at a fixed inclination for purposes of this invention, and is held at the inclination shown by one or more braces 36. Out warclly beyond the load wheels, there is a spaced pair of safety wheels 38 which are normally spaced slightly above the contact plane of the wheels 10, 12, and 14. Such safety wheels 38 come into contact with the supporting surface and provide additional support against tipping when the load flexes the tires on the load wheels 10, or tends to tip the truck about the axis of those wheels 10.

As shown in Fig. 9, the lift mechanism. 31 comprises a fixed section 3 formed of two spaced channel members 40 disposed to open inwardly, interconnected at their upper ends by a ribbed cross plate 42, and suitably interconnected. at the lower ends by supports which are not shown. An intermediate lift section 43 is nested between the channel members 4%) and comprises a pair of spaced and inwardly open channel members a l rigidly interconnected by cross members 46 adjacent one face of the section-the upper face in Fig. 9 and the lower face in Fig. l. The intermediate lift section 43 is supported at its lower end by a pair of rollers 48 riding in the channel members 40, and is supported at its upper end by sliding. engagement with the ribbed cross plate 42. It is lifted with respect to the fixed section by a hydraulic cylinder carried beside and below (above in Fig. 9) the fixed section 34. The piston rod 51 of that cylinder carries a pair of sprockets or sheaves 52 which operatively engage a pair of chains 53 secured at their lower ends to fixed points on the cylinder 50 and secured at their other ends to a cross member 46 at the lower end of the intermediate section 43.

The upper section 32 of the lift mechanism 30 com prises a pair of spaced L-shaped members 56 whose parallel legs extend into nesting relation between the channel members 44 of the intermediate section, and each of which carries a pair of spaced rollers 58 riding in the channel of its adjacent channel member 44. These L-shaped members 56 support a sub-frame 60 which has a lower leg portion 62 positioned adjacent the upper face ,(the bottom face in Fig. 9) of the lift mechanism 30 and extending upward beyond the top-most rollers 58. At the upper end of this leg section 62, which lies above the intermediate section 43 in raised position, the sub-frame carries a horizontal leg portion 64 on which the platform structure is mounted. The top-most lift section 32 is raised with respect to the intermediate section 43 by a hydraulic cylinder 66 carried by the intermediate section 43 in nested position within the lift mechanism, as shown in Fig. 9. Its piston rod 67 carries a pair of sprockets or sheaves 68 engaged in a pair of chains 70 fixed at their lower ends to a bracket '71 carried by the cylinder 66, and connected at their other ends to a cross member 63 at the lower end of the sub-frame 66. Extension of the piston rod 67 lifts the sub-frame 66 with respect to the intermediate section 43. Consecutive operation of the two hydraulic cylinders 66 and 50 lifts the top-most lift section 32 from the lowered position shown in broken lines in Fig. 1 to the extreme raised position shown in full lines in Fig. l.

The platform 86 is carried on a pair of spaced channel members 82 disposed in inwardly open position at the opposite side edges of an interconnecting floor structure 84, as is best seen in Figs. 7 and 8. To support the platform for traversing movement with respect to the upper lift section 32, the lower flanges of the platform side supports 82 are received between upper pairs of rollers 86 and lower pairs of rollers 88 carried by the horizontal leg 64 of the sub-frame 60, and the platform side channels 82 are held in engagement and alignment with these supporting rollers by vertical rollers 90 bearing against the outer faces of the channel members 82. The traverse movement of the platform is desirably powor operated. To this end, the sub-frame 60 carries an electric motor 92 which drives a gear reducer 94 connected to drive a sprocket 96. A chain 98 extends from end to end beneath the platform 86 and is suitably held in engagement with the sprocket 96 as by a shoe 99. Power for the electric motor 92 is supplied by the battery 18 through an extendable cable 190 wound on a springreturn reel 102. Operation of the traversing motor 92 is controlled by a pair of push buttons 1% positioned for operation by a service man on the platform 3% The platform 80 has upright side frames 166 and 108. The side frame 106 carries a tray 110 for service parts and equipment, and may carry a rack 111 as for replacement light tubes. The side frame 1&8 carries a compartmented wash tank 112, desirably having three compartments for wash and rinse waters. Each compartment is provided with a separate drain controlled by a valve 114 and draining to a drain trough 116. The drain trough 116 is sloped downward and at its rear end carries a dependent drain pipe 118, whose lower end is positioned to enter a drain receptacle 119 on the water storage tank described below when the platform is in lowered position as shown in dotted lines in Fig. 1.

Desirably, the front end of the platform 80 (to the left of Figs. 1 and 3), carries a hinged extension platform 120, hinged to the front edge of the main platform 80 and held in horizontal position by a pair of chains 122.

Upon lowering movement of the platform to a point below the upper end of the main lift section 34, the extension platform 12% strikes the lift mechanism and is lifted thereby to the storage position indicated in dotted lines in Fig. 1. The platform also desirably carries a pair of drop cloth wings 124. These are lightweight frames covered with a suitable material such as canvas, and pivoted to the side edges of the platform 80. They are supported in operative position by chains 126, and may be folded upward against the sides of the platform structure when the apparatus is moved from place to place.

The commercial truck used in the apparatus of the invention normally comes equipped with a counterweight carried by a sub-frame 132 supported by the load wheels 10 and the caster wheels 14. This counterweight may be retained. The main counterbalancing weight, however, is provided by a water tank 136 mounted at the opposite end of the truck frame from the lift and platform apparatus 30-80. As shown in Figs 1, 3, and 6, this tank 134 is generally horseshoe shaped and is positioned about the motor-drive unit 16. t may rest on the counterweight 13d and may be held in place by pins engaged downwardly through sleeves 136 carried at the inner end of the tank. The tank comprises a bottom wall 138, an outer curved side wall 140, an inner curved side wall 141, and two end walls 142, integrally joined in fluid-tight relationship. A cover plate 144 is removably attached to the flange at the upper edge of the tank. A flexible bladder 146, of rubber or similar material, and

shaped to conform with the tank is received within thc tank to form an inner compartment therein and to partition its contained space from the space or outer compartment between the bladder and the tank walls. When the bladder is full and the outer compartment empty, the bladder occupies substantially the entire space within the tank.

The bladder 146 has a bottom opening whose edges are sealed to a fitting 143 connected through a side-outlet fitting 15f) to a T-fitting 152. A fill pipe 154 is threaded into the top of the fitting 152 and a drain valve 156 is connected to the bottom of that fitting 152. As is shown in Figs. 4 to 6, the side opening of the fitting 156i is connected by a pipe 153 containing a valve 166 to the inlet side of a pump 162. The bottom 138 of the tank 134- contains an outlet fitting 164 connected through a side-outlet fitting to a drain valve 166 and the side-outlet is connected by a pipe 168 containing a valve 171) to the inlet of the pump 162. By optional opening of the valves and 170, water may be supplied to the pump 162 either from the inner compartment within the bladder or from the outer compartment outside the bladder. By opening the valve 156, the bladder may be drained, and by opening the valve 166, the tank outside the bladder may be drained.

The cover plate 144 of the tank carries the inlet fitting 119, which leads to the space within the tank but outside the bladder 146. To insure that water above the bladder 146 may reach the drain valve 166, there are one or more perforated baffle plates 172 fixed against the inside of the tank wall 146 to form an open channel leading to the bottom of the tank.

The pump 162 is driven by an electric motor 17-4, controlled by a push button 176 mounted on a post 177 in position to be operated from the platform 3%. The outlet 178 from the pump 162 is connected to a hose 180 having a hook shaped end fitting 182 normally carried on a support at the upper end of the post 177 in position for use by the operator to fill the wash tanks 112.

The control and supply system for the hydraulic lift mechanism is'shown in Fig. 10. A reservoir 184 for hydraulic fluid is connected by a pipe 185 to a pump 186 driven'by an electric motor 187. The outlet of the pump is connected by a pipe 188 to an electrically operated valve 190, and that valve 190 is also connected by a return pipe 191 to the reservoir pipe 185. The valve 196 controls flow to and from a pipe 192. connected to the lower end of the fixed lift cylinder 50 by a pipe 193, and to the lower end of the movable lift cylinder 66 through a flexible hose 194.

The valve 190 contains a 'shiftable valve member 189 having a central land 198, which is spring pressed to a neutral position in which the land 193 closes the port leading to the pipe 192. For operation, the valve member 189 is connected through a link 199 to a solenoid armature 20d, arranged to be actuated upward by a solenoid coil 202 and to be actuated downward by a solenoid coil 264*. A stop 2&6 movable with the valve member 198 is arranged to close a normally open switch 208 when the valve is in raised position, to close the circuit 210 leading from the truck battery 18 to the motor 187. The coils 202 and 204 are connected by a wire 214 to the battery 18, and their opposite ends are connected by wires 216 to a cable 218 carried by a spring return reel 22% mounted beside the reel 102 shown in Fig. l. The cable 21% leads to a switch box 222 carried by the platform 89, and contains an Up push button 223 and a Down push button 224 for selectively closing the circuits of the solenoids 262 and 294.

The operation of this lift supply and control system is as follows:

As "shown in Fig. 10, the valve land 193 is in neutral position and it is assumed that the two cylinders 50- and 66 are in retracted positions. The motor circuit and the two solenoid circuits are open. To lift the platform, the Up button 223 on the platform 80 is depressed, closing the circuit to the solenoid 202. This actuates the armature Zfiil upward, to carry the valve land 198 upward and connect the pump discharge pipe 188 to the cylinder supply pipe 192, and the concurrent upward movement of the stop 206 closes the switch 208 to energize the pump motor 7137. The pump then forces bydraulic fluid through the pipe 138 and valve 190 to the lower ends of the two cylinders 50 and 66-. Since the cylinder 66 carried by the intermediate lift section 43 supports the least weight, this cylinder acts first, and carries the top-most lift section 32 to its extreme upward position with respect to the intermediate lift section 43L This positions the platform above the still retracted lift section 34, which permits the platform to be traversed above the underiying lift mechanism if desired. If the hydraulic pump is continued in operation after the lift cyiinder 66 has reached the limit of its movement, the hydraulic pressure then actuates the fixed cylinder 50 to lift the intermediate lift section 43 with respect to the fixed section 34, to raise the platform higher, as to the position shown in dotted lines in Fig. 1. Release of the push button 223 at any point in this cycle de-energizes the solenoid 292 and permits the valve land 198 to return to neutral position, to close the pipe 192 and lock the cylinders 50 and do in their existing condition. To move the platform downward, the push button 224 is depressed, which energizes the solenoid coil 294 to move the armature 204i and the valve land 298 downward, and this connects the cylinder supply pipe 192 to the return line 191 leading to the reservoir, permitting the cylinders to collapse and the lift to move to lowered position.

The supply and control system for the traverse motor 92 for the platform 8% is shown in Fig. 11. Power from the battery 13 is supplied to the platform through the cable 1&0 held on the reel 192, which leads to a reversing, relay 23%) carried by the platform 3d.

The reversing relay 23%) is controlled for outward move ment by a circuit which includes a normally closed limit switch 236 mounted on the sub-frame 60 and arranged to be actuated to open position by engagement with one of the side members 44 of the intermediate lift section 43 whenever the platform lies below the upper end of that intermediate lift section. That circuit also includes a limit switch 234, and an Out button 238 carried :by the switch boxv 104. The control circuit for moving the platform inward is controlled by the Back button 240 of the switch box 104 and leads through a limit switch 232 to the reversing relay 230. If the platform is at an elevation above the intermediate lift section 43, so that the limit switch 236 is closed, actuation of the Out button 238 will cause the reversing relay to actuate the motor in a direction to move the platform outward, to the left in Fig. 1, until it reaches the limit of its movement. At that limit, a stop 235 actuates a limit lever 237 to open the limit switch 234 and deenergize the relay 230 to stop the motor 92. Actuation of the back button 240 will actuate the reversing relay to energize the motor for movement in a direction to move the platform rearward, to the right in Fig. l, to the limit of its movement. At that limit, the stop 233 will engage the limit lever 237 to open limit switch 232 and tie-energize the relay 230 to stop the motor 92.

Operation of the device as a whole is as follows:

The bladder 146 in the tank 134 is filled with wash water through the till pipe 154, and when so filled, the bladder will occupy substantially the entire space within the tank. 134. Conveniently, the bladder and tank are of the size to contain. about gallons of water. The workman then mounts the platform, and by operation of the tiller handle 20 and push buttons 21 releases the brakes of the truck and drives it to a desired position. He fills the wash tank 112 from the hose 180, by pressing the control button 176 for the water pump motor 174, which pumps water from within the bladder 146 by way of the pipe 158. With the wash tanks 112 filled with water, and with the necessary equipment on the. platform, the workman then actuates the up-button 223 of the lift control switch box 222, to actuate the hydraulic pump 186 and lift thepla-tform to the desired elevation. With the pla form at a desired elevation above the upper end of the intermediate lift section 43, the workman then actuates the push button 238 of the traverse control box 104, to actuate the traverse motor 92 and move the platform to the desired projected position, as to that shown in full lines in Fig. 1. With the platform thus raised and projected, it lies in an over-hanging position well beyond the supporting wheels of the truck. It is counter-balanced in this position by the weight of the truck itself, by the counter-weight at the oposite end of the truck, and largely by the 100 gallons of water in the tank 134.

Upon completion of a washing operation at one place, the operator actuates the traverse Back button 240 to move the platform inward, to the dotted line position shown at the top of Fig. l, and then actuates the Down button 224 of the lift control 222 to lower the platform to the broken line. position shown in Fig. l. As the platform reaches thisposition, the lower end of the drain pipe 118 enters the drain fitting 119. The workman can then open one or more of the drain valves 114, and the water will drain from the tank 112 to the trough 1E6, through the drain pipe 118 and into the tank 134. This dirty water, however, will not be mixed with the clean water within: the bladder 146, but will be received between the bladder 146 and the outer walls of the tank. Fresh water can then be pumped from the bladder 146 to replenish the wash tanks 112, and the full operation repeated.

All movements of the truck and of the platform are within the control of the workman on the platform, and he can move from one work position to another without leaving the platform. The ballast tank provides a large supply of clean wash water, and an equally large receptacle for disposal of the water after use. The workman thus is-enabled to proceed efficiently with washing operations, without wasting time and effort in obtaining fresh supplies, disposing of waste, or setting up equipment.

When the entire supply of fresh water in the bladder 146 has been used, the operator can move the truck to a convenient position for draining the dirty water and replenishing the fresh water, and at that point, he opens the drainvalve 166 to release the dirty water from the tank. Alternatively, he may open the valve 170 and operate the pump 162 to pump the dirty water from the tank to any .available drain. He then refills the bladder 146 with fresh water and is ready to continue his work.

I claim as my invention:

1. Over-head service apparatus, comprising a mobile carrier, a platform support on said carrier, a platform carried thereby and movable relative thereto to a projected over-hanging position, a water ballast tank for counterbalancing the over-hanging platform and containing a movable partition to form two compartments therein of relatively variable capacity, means to supply fresh water from one compartment to the platform, and means to return water from the platform to the second compartment, each of said water-supply means and said water-return means being operable in at least one position of the platform.

2. Overhead service apparatus, comprising a mobile carrier, a platform support on said carrier, a platform carried thereby and movable relative thereto to a projected over-hanging position, a water ballast tank for counterbalancing the over-hanging platform and containing a flexible bladder dividing said tank into inner and outer compartments, means to supply fresh water from one compartment to the platform, and means to return water from the platform to the second compartment, each of said water-supply means and said water-return means being operable in at least one position of the platform.

3. Service apparatus, comprising a mobile carrier, a wash tank carried by the carrier, 2 water tank carried by the carrier, a movable partition dividing said water tank to form two compartments therein of relatively variable size, means to supply water from one compartment to the wash tank, and means to return water from the wash tank to the other compartment.

4. Over-head service apparatus, comprising a mobile carrier, an extensible platform support on said carrier, a platform carried by said support and having a retracted position and extensible by said support from said retracted position to projected service positions, a compartmented ballast tank on said carrier, a wash tank movable with said platform, a pump operable from said platform in retracted position to supply water from one ballast tank compartment to said wash tank, and means operable in platform retracted position to return water from the wash tank to a separate ballast-tank compartment.

5. Over-head service apparatus, comprising a mobile carrier, an extendible platform support on said carrier, :a platform carried by said support and having a retracted position and extendible by said support from said retracted position to projected service positions, a compartmented ballast tank on said carrier, a wash tank movable with said platform, means to supply water from one ballast-tank compartment to said wash tank, a drain carried with said wash tank, a fixed drain receptacle leading to a separate ballast-tank compartment, said drain being positioned for discharge to said receptacle when said platform is in retracted position.

6. Over-head service apparatus, comprising a mobile carrier, service lift apparatus at one end of the carrier and including a platform having an over-hanging position, a water-receptacle associated therewith, a drive unit adjacent the opposite end of the carrier, a U-shaped ballast tank about the drive unit, and means to supply water from said tank to said water-use equipment and means to return used water thereto.

7. Over-head service equipment as defined in claim 6, in which said tank contains a movable partition dividing said tank int-o fresh-water and used-water compartments of relatively variable sizes.

8. Service apparatus, comprising a mobile carrier, a

work platform carried by the carrier and having an overhanging work position, apparatus carried by the carrier which requires a source of relatively small quantities of liquid for use therein and the discharge of used liquid and its replacement with fresh liquid, and a ballast tank of relatively large liquid volume positioned to counterbalance the platform in its overhanging work position and having a partition therein which divides the tank into two compartments .of relatively variable size, an outlet from one compartment for supplying fresh liquid therefrom to said liquid-using apparatus, and an inlet to the other compartment for returning to said tank the used liquid discharged from the said liquid-using apparatus, whereby said tank serves as a source of fresh liquid and a receptacle for used liquid and is maintained at a substantially constant counter-balancing weight during use of the fresh liquid originally contained in the tank.

9. Overhead service apparatus, comprising a mobile carrier, an outwardly inclined lift column adjacent one end thereof, a platform support carried by said lift column and movable longitudinally thereof, a riding platform supported on said support for horizontal movement thereon and adapted to be ridden by a workman, said platform having a retracted position on the support in which it clears said column and said support being movable downward on the column to lower said platform to a transport position at a level below the top of the column and at least partially overlying the carrier, and said support having an elevated position in which it disposes said platform at a level above the top of the column and said platform being horizontally movable at said level across the column to an extended overhanging posi tion with respect to the carrier, said carrier including means for counter-balancing the lift column and extended platform.

10. Overhead service apparatus according to claim 9 in which said lift column is extensible when said support is in elevated position.

11. Overhead service apparatus according to claim 10 with the addition of power means operable when said platform is in said column-clearing position to move said support on said column and to the said elevated position, and power means operable when said support is in said elevated position to extend said column.

12. Overhead service apparatus according to claim 11 with the addition of power means operable when said support is in said elevated position to move said platform horizontally on said support, and means to inactivate said last-named power means when the platform is below the top of the column.

13. Overhead service apparatus according to claim 12 with the addition of controls operable from said platform for actuating said several power means.

14. Overhead service apparatus, comprising a mobile carrier, an upstanding lift column thereon, a platform support carried by said lift column and movable upward and downward thereof along one face of the column, a riding platform supported for horizontal movement on said support and adapted to be ridden by a workman, said support being movable to a position in which it positions the platform at a level above the top of the column, said riding platform in said position being traversable over the top of the column to an extended overhanging position, said platform having a retracted position-on the support in which said column can pass through the plane of the platform and said support being movable downward when the platform is in said retracted position to lower the platform below the top of the column.

15. Overhead service apparatus according to claim 14 in which said platform carries a pivoted section which normally overlies said column when the platform is in its retracted position and which pivots upward to pass the column through the plane of the platform as the platform is lowered.

16. Over-head service equipment, comprising a mobile carrier having load wheels adjacent one end thereof and a steerable wheel adjacent the opposite end thereof, an outwardly inclined lift mechanism supported adjacent said load wheels, an elevator platform carried by the lift mechanism and traversable from the carrierside of said lift mechanism to a position projecting outwardly beyond the opposite side thereof, and a safety wheel carried by the carrier outward in the direction of platform projection, said safety wheel being normally spaced from the contact plane of the load Wheels and moving thereto upon incipient tipping movement of the carrier about said load wheels.

17. Over-head service equipment, comprising a mobile carrier, an upstanding lift column adjacent one end thereof, an elevator platform support carried by said lift column for movement upward and downward along one face thereof, a platform horizontally movable on said support, said support having a lowered position in which said column would interfere with movement of the platform on the support and having an elevated position in which the platform clears the column and is movable on the support over the column, a platform drive, and means to inactivate the platform drive when the platform is below a clearance level with respect to the lift column.

18. Overhead service equipment, comprising a mobile carrier, an upstanding extensible lift column at one end thereof and having an inner face facing toward the carrier and an outer face facing away fnom the carrier, a platform support carried at one of said faces of the column, means to move said support along said face between a lowered position in which it lies below the top of the column and a raised position in which its upper portion lies above the column, means to extend the column while said support is in said raised position, a platform on said support, said platform having a first portion which in a normal position lies at the inner-face side of the column and when lowered substantially overlies the carrier and having a second portion which in normal position with said support in said raised position overlies the column, said second portion being pivoted :on an axis spaced from one face of the column and movable upwardly about said axis to a column-clearing position when said platform support is moved to its lowered position, said two platform portions being mounted on said platform support by traversing mechanism operative in the raised position of the support to traverse the platform across the top of the column to an overhanging position projecting beyond the outer face of the column.

References Cited in the file of this patent UNITED STATES PATENTS 415,667 Edwards Nov. 19, 1889 689,001 Hill Dec. 17, 1901 803,717 Schwarz et a1. Nov. 7, 1905 1,053,080 Whitney Feb. 11, 1913 1,474,249 Ferraro Nov. 13, 1923 1,699,544 Rohlfing Jan. 22, 1929 1,835,132 Anania Dec. 8, 1931 2,376,875 Honig May 29, 1945 2,423,167 Aune July 1, 1947 2,468,378 Scofield Apr. 26, 1949 2,472,887 Core June 14, 1949 2,609,118 Cattaneo Sept. 21, 1952 FOREIGN PATENTS 608,007 France Apr. 10, 1926 251,777 Italy July 10, 1926 

